Radical oxidation process for fabricating a nonvolatile charge trap memory device

ABSTRACT

A method for fabricating a nonvolatile charge trap memory device is described. The method includes providing a substrate having a charge-trapping layer disposed Thereon. A portion of the charge-trapping layer is then oxidized to form a blocking Dielectric layer above the charge-trapping layer by exposing the charge-trapping layer to a radical oxidation process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/940,139, filed May 25, 2007, and U.S. Provisional Application No.60/986,637, filed Nov. 9, 2007, the entire contents of which are herebyincorporated by reference herein.

TECHNICAL FIELD

Embodiments of the present invention are in the field of SemiconductorFabrication and, in particular, Semiconductor Device Fabrication.

BACKGROUND

For the past several decades, the scaling of features in integratedcircuits has been a driving force behind an ever-growing semiconductorindustry. Scaling to smaller and smaller features enables increaseddensities of functional units on the limited real estate ofsemiconductor chips. For example, shrinking transistor size allows forthe incorporation of an increased number of memory devices on a chip,lending to the fabrication of products with increased capacity. Thedrive for ever-more capacity, however, is not without issue. Thenecessity to optimize the performance of each device becomesincreasingly significant.

Non-volatile semiconductor memories typically use stacked floating gatetype field-effect-transistors. In such transistors, electrons areinjected into a floating gate of a memory cell to be programmed bybiasing a control gate and grounding a body region of a substrate onwhich the memory cell is formed. An oxide-nitride-oxide (ONO) stack isused as either a charge storing layer, as in asemiconductor-oxide-nitride-oxide-semiconductor (SONOS) transistor, oras an isolation layer between the floating gate and control gate, as ina split gate flash transistor. FIG. 1 illustrates a cross-sectional viewof a conventional nonvolatile charge trap memory device.

Referring to FIG. 1, semiconductor device 100 includes a SONOS gatestack 104 including a conventional ONO portion 106 formed over a siliconsubstrate 102. Semiconductor device 100 further includes source anddrain regions 110 on either side of SONOS gate stack 104 to define achannel region 112. SONOS gate stack 104 includes a poly-silicon gatelayer 108 formed above and in contact with ONO portion 106. Poly-silicongate layer 108 is electrically isolated from silicon substrate 102 byONO portion 106. ONO portion 106 typically includes a tunnel oxide layer106A, a nitride or oxy-nitride charge-trapping layer 106B, and a topoxide layer 106C overlying nitride or oxy-nitride layer 106B.

One problem with conventional SONOS transistors is the poor dataretention in the nitride or oxy-nitride layer 106B that limitssemiconductor device 100 lifetime and its use in several applicationsdue to leakage current through the layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a conventional nonvolatilecharge trap memory device.

FIG. 2 illustrates a cross-sectional view of an oxidation chamber of abatch-processing tool, in accordance with an embodiment of the presentinvention.

FIG. 3 depicts a Flowchart representing a series of operations in amethod for fabricating a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

FIG. 4A illustrates a cross-sectional view of a substrate having acharge-trapping layer formed thereon, corresponding to operation 302from the Flowchart of FIG. 3, in accordance with an embodiment of thepresent invention.

FIG. 4B illustrates a cross-sectional view of a substrate having acharge-trapping layer with a blocking dielectric layer formed thereon,corresponding to operation 304 from the Flowchart of FIG. 3, inaccordance with an embodiment of the present invention.

FIG. 5 depicts a Flowchart representing a series of operations in amethod for fabricating a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

FIG. 6A illustrates a cross-sectional view of a substrate, correspondingto operation 502 from the Flowchart of FIG. 5, in accordance with anembodiment of the present invention.

FIG. 6B illustrates a cross-sectional view of a substrate having a firstdielectric layer formed thereon, corresponding to operation 504 from theFlowchart of FIG. 5, in accordance with an embodiment of the presentinvention.

FIG. 6C illustrates a cross-sectional view of a substrate having acharge-trapping layer formed thereon, corresponding to operation 508from the Flowchart of FIG. 5, in accordance with an embodiment of thepresent invention.

FIG. 6D illustrates a cross-sectional view of a substrate having acharge-trapping layer with a blocking dielectric layer formed thereon,corresponding to operation 510 from the Flowchart of FIG. 5, inaccordance with an embodiment of the present invention.

FIG. 6E illustrates a cross-sectional view of a nonvolatile charge trapmemory device, in accordance with an embodiment of the presentinvention.

FIG. 7A illustrates a cross-sectional view of a substrate includingfirst and second exposed crystal planes, in accordance with anembodiment of the present invention.

FIG. 7B illustrates a cross-sectional view of the substrate includingfirst and second crystal planes and having a dielectric layer formedthereon, in accordance with an embodiment of the present invention.

FIG. 8 illustrates an arrangement of process chambers in a cluster tool,in accordance with an embodiment of the present invention.

FIG. 9 depicts a Flowchart representing a series of operations in amethod for fabricating a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

FIG. 10A illustrates a cross-sectional view of a substrate, inaccordance with an embodiment of the present invention.

FIG. 10B illustrates a cross-sectional view of a substrate having atunnel dielectric layer formed thereon, corresponding to operation 402from the Flowchart of FIG. 4, in accordance with an embodiment of thepresent invention.

FIG. 10C illustrates a cross-sectional view of a substrate having acharge-trapping layer formed thereon, corresponding to operation 406from the Flowchart of FIG. 4, in accordance with an embodiment of thepresent invention.

FIG. 10D illustrates a cross-sectional view of a substrate having a topdielectric layer formed thereon, corresponding to operation 408 from theFlowchart of FIG. 4, in accordance with an embodiment of the presentinvention.

FIG. 10E illustrates a cross-sectional view of a nonvolatile charge trapmemory device, in accordance with an embodiment of the presentinvention.

FIG. 11 depicts a Flowchart representing a series of operations in amethod for fabricating a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

FIG. 12A illustrates a cross-sectional view of a substrate having atunnel dielectric layer formed thereon, corresponding to operation 602from the Flowchart of FIG. 6, in accordance with an embodiment of thepresent invention.

FIG. 12B illustrates a cross-sectional view of a substrate having anoxygen-rich silicon oxy-nitride portion of a charge-trapping layerformed thereon, corresponding to operation 606 from the Flowchart ofFIG. 6, in accordance with an embodiment of the present invention.

FIG. 12C illustrates a cross-sectional view of a substrate having asilicon-rich silicon oxy-nitride portion of a charge-trapping layerformed thereon, corresponding to the operation 610 from the Flowchart ofFIG. 6, in accordance with an embodiment of the present invention.

FIG. 12D illustrates a cross-sectional view of a substrate having a topdielectric layer formed thereon, corresponding to operation 612 from theFlowchart of FIG. 6, in accordance with an embodiment of the presentinvention.

FIG. 12E illustrates a cross-sectional view of a nonvolatile charge trapmemory device, in accordance with an embodiment of the presentinvention.

FIG. 13A illustrates a cross-sectional view of a substrate includingfirst and second exposed crystal planes, in accordance with anembodiment of the present invention.

FIG. 13B illustrates a cross-sectional view of the substrate includingfirst and second crystal planes and having a dielectric layer formedthereon, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Methods to fabricate a nonvolatile charge trap memory device aredescribed herein. In the following description, numerous specificdetails are set forth, such as specific dimensions, in order to providea thorough understanding of the present invention. It will be apparentto one skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-knownprocessing steps, such as patterning steps or wet chemical cleans, arenot described in detail in order to not unnecessarily obscure thepresent invention. Furthermore, it is to be understood that the variousembodiments shown in the Figures are illustrative representations andare not necessarily drawn to scale.

Disclosed herein is a method to fabricate a nonvolatile charge trapmemory device. A substrate may first be provided having acharge-trapping layer disposed thereon. In one embodiment, a portion ofthe charge-trapping layer is then oxidized to form a blocking dielectriclayer above the charge-trapping layer by exposing the charge-trappinglayer to a radical oxidation process.

Formation of a dielectric layer by a radical oxidation process mayprovide higher quality films than processes involving steam growth, i.e.wet growth processes. Furthermore, a radical oxidation process carriedout in a batch-processing chamber may provide high quality films withoutimpacting the throughput (wafers/Hr) requirements that a fabricationfacility may require. By carrying out the radical oxidation process attemperatures compatible with such a chamber, such as temperaturesapproximately in the range of 600-900 degrees Celsius, the thermalbudget tolerated by the substrate and any other features on thesubstrate may not be impacted to the extent typical of processes over1000 degrees Celsius. In accordance with an embodiment of the presentinvention, a radical oxidation process involving flowing hydrogen (H₂)and oxygen (O₂) gas into a batch-processing chamber is carried out toeffect growth of a dielectric layer by oxidation consumption of anexposed substrate or film. In one embodiment, multiple radical oxidationprocesses are carried out to provide a tunnel dielectric layer and ablocking dielectric layer for a non-volatile charge trap memory device.These dielectric layers may be of very high quality, even at a reducedthickness. In one embodiment, the tunnel dielectric layer and theblocking dielectric layer are both denser and are composed ofsubstantially fewer hydrogen atoms/cm³ than a tunnel dielectric layer ora blocking dielectric layer formed by wet oxidation techniques. Inaccordance with another embodiment of the present invention, adielectric layer formed by carrying out a radical oxidation process isless susceptible to crystal plane orientation differences in thesubstrate from which it is grown. In one embodiment, the corneringeffect caused by differential crystal plane oxidation rates issignificantly reduced by forming a dielectric layer via a radicaloxidation process.

A portion of a nonvolatile charge trap memory device may be fabricatedby carrying out a radical oxidation process in a process chamber. Inaccordance with an embodiment of the present invention, the processchamber is a batch-processing chamber. FIG. 2 illustrates across-sectional view of an oxidation chamber of a batch-processing tool,in accordance with that embodiment. Referring to FIG. 2, abatch-processing chamber 200 includes a carrier apparatus 204 to hold aplurality of semiconductor wafers 202. In one embodiment, thebatch-processing chamber is an oxidation chamber. In a specificembodiment, the process chamber is a low-pressure chemical vapordeposition chamber. The plurality of semiconductor wafers 202 may bearranged in such a way as to maximize exposure of each wafer to aradical oxidation process, while enabling the inclusion of a reasonablenumber of wafers (e.g. 25 wafers), to be processed in a single pass. Itshould be understood, however, that the present invention is not limitedto a batch-processing chamber.

In an aspect of the present invention, a portion of a nonvolatile chargetrap memory device is fabricated by a radical oxidation process. FIG. 3depicts a Flowchart representing a series of operations in a method forfabricating a nonvolatile charge trap memory device, in accordance withan embodiment of the present invention. FIGS. 4A-4B illustratecross-sectional views representing operations in the fabrication of anonvolatile charge trap memory device, in accordance with an embodimentof the present invention.

FIG. 4A illustrates a cross-sectional view of a substrate having acharge-trapping layer formed thereon, corresponding to operation 302from the Flowchart of FIG. 3, in accordance with an embodiment of thepresent invention. Referring to operation 302 of Flowchart 300 andcorresponding FIG. 4A, a substrate 400 is provided having acharge-trapping layer disposed thereon. In an embodiment, thecharge-trapping layer has a first region 404A and a second region 404Bdisposed above substrate 400. In one embodiment, a dielectric layer 402is disposed between substrate 400 and the charge-trapping layer, asdepicted in FIG. 4A. The charge-trapping layer may be composed of amaterial and have a thickness suitable to store charge and, hence,change the threshold voltage of a subsequently formed gate stack. In anembodiment, region 404A of the charge-trapping layer will remain as anintact charge-trapping layer following subsequent process operations.However, in that embodiment, region 404B of the as-formedcharge-trapping layer will be consumed to form a second dielectriclayer, above region 404A.

FIG. 4B illustrates a cross-sectional view of a substrate having acharge-trapping layer with a blocking dielectric layer formed thereon,corresponding to operation 304 from the Flowchart of FIG. 3, inaccordance with an embodiment of the present invention. Referring tooperation 304 of Flowchart 300 and corresponding FIG. 4B, a blockingdielectric layer 406 is formed on charge-trapping layer 404. Inaccordance with an embodiment of the present invention, blockingdielectric layer 406 is formed by oxidizing region 404B of thecharge-trapping layer by exposing the charge-trapping layer to a radicaloxidation process. In that embodiment, region 404A of the originalcharge-trapping layer is now labeled as charge-trapping layer 404.

Blocking dielectric layer 406 may be composed of a material and have athickness suitable to maintain a barrier to charge leakage withoutsignificantly decreasing the capacitance of a subsequently formed gatestack in a nonvolatile charge trap memory device. In a specificembodiment, region 404B is a silicon-rich silicon oxy-nitride regionhaving a thickness approximately in the range of 2-3 nanometers and isoxidized to form blocking dielectric layer 406 having a thicknessapproximately in the range of 3.5-4.5 nanometers. In that embodiment,blocking dielectric layer 406 is composed of silicon dioxide.

Blocking dielectric layer 406 may be formed by a radical oxidationprocess. In accordance with an embodiment of the present invention, theradical oxidation process involves flowing hydrogen (H₂) and oxygen (O₂)gas into a furnace, such as the batch processing chamber 200 describedin association with FIG. 2. In one embodiment, the partial pressures ofH₂ and O₂ have a ratio to one another of approximately 1:1. However, inan embodiment, an ignition event is not carried out which wouldotherwise typically be used to pyrolyze the H₂ and O₂ to form steam.Instead, H₂ and O₂ are permitted to react to form radicals at thesurface of region 404B. In one embodiment, the radicals are used toconsume region 404B to provide blocking dielectric layer 406. In aspecific embodiment, the radical oxidation process includes oxidizingwith a radical such as, but not limited to, an OH radical, an HO₂radical or an O diradical at a temperature approximately in the range of600-900 degrees Celsius. In a particular embodiment, the radicaloxidation process is carried out at a temperature approximately in therange of 700-800 degrees Celsius at a pressure approximately in therange of 0.5-5 Torr. In one embodiment, the second radical oxidationprocess is carried out for a duration approximately in the range of100-150 minutes.

Referring to operation 306 of Flowchart 300, blocking dielectric layer406 may be further subjected to a nitridation process in the firstprocess chamber. In accordance with an embodiment of the presentinvention, the nitridation process includes annealing blockingdielectric layer 406 in an atmosphere including nitrogen at atemperature approximately in the range of 700-800 degrees Celsius for aduration approximately in the range of 5 minutes-60 minutes. In oneembodiment, the atmosphere including nitrogen is composed of a gas suchas, but not limited to, nitrogen (N₂), nitrous oxide (N₂O), nitrogendioxide (NO₂), nitric oxide (NO) or ammonia (NH₃). Alternatively, thisnitridation step, i.e. operation 306 from Flowchart 300, may be skipped.

In an aspect of the present invention, both a tunnel dielectric layerand a blocking dielectric layer may be formed by radical oxidationprocesses. FIG. 5 depicts a Flowchart 500 representing a series ofoperations in a method for fabricating a nonvolatile charge trap memorydevice, in accordance with an embodiment of the present invention. FIGS.6A-6E illustrate cross-sectional views representing operations in thefabrication of a nonvolatile charge trap memory device, in accordancewith an embodiment of the present invention.

FIG. 6A illustrates a cross-sectional view of a substrate, correspondingto operation 502 from the Flowchart of FIG. 5, in accordance with anembodiment of the present invention. Referring to operation 502 ofFlowchart 500 and corresponding FIG. 6A, a substrate 600 is provided ina process chamber.

Substrate 600 may be composed of a material suitable for semiconductordevice fabrication. In one embodiment, substrate 600 is a bulk substratecomposed of a single crystal of a material which may include, but is notlimited to, silicon, germanium, silicon-germanium or a III-V compoundsemiconductor material. In another embodiment, substrate 600 includes abulk layer with a top epitaxial layer. In a specific embodiment, thebulk layer is composed of a single crystal of a material which mayinclude, but is not limited to, silicon, germanium, silicon-germanium, aIII-V compound semiconductor material or quartz, while the top epitaxiallayer is composed of a single crystal layer which may include, but isnot limited to, silicon, germanium, silicon-germanium or a III-Vcompound semiconductor material. In another embodiment, substrate 600includes a top epitaxial layer on a middle insulator layer which isabove a lower bulk layer. The top epitaxial layer is composed of asingle crystal layer which may include, but is not limited to, silicon(i.e. to form a silicon-on-insulator (SOI) semiconductor substrate),germanium, silicon-germanium or a III-V compound semiconductor material.The insulator layer is composed of a material which may include, but isnot limited to, silicon dioxide, silicon nitride or silicon oxy-nitride.The lower bulk layer is composed of a single crystal which may include,but is not limited to, silicon, germanium, silicon-germanium, a III-Vcompound semiconductor material or quartz. Substrate 600 may furtherinclude dopant impurity atoms.

FIG. 6B illustrates a cross-sectional view of a substrate having adielectric layer formed thereon, corresponding to operation 504 from theFlowchart of FIG. 5, in accordance with an embodiment of the presentinvention. Referring to operation 504 of Flowchart 500 and correspondingFIG. 6B, substrate 600 is subjected to a first radical oxidation processto form a first dielectric layer 602.

First dielectric layer 602 may be composed of a material and have athickness suitable to allow charge carriers to tunnel into asubsequently formed charge-trapping layer under an applied gate bias,while maintaining a suitable barrier to leakage when a subsequentlyformed nonvolatile charge trap memory device is unbiased. Firstdielectric layer 602 may be referred to in the art as a tunneldielectric layer. In accordance with an embodiment of the presentinvention, first dielectric layer 602 is formed by an oxidation processwhere the top surface of substrate 600 is consumed. Thus, in anembodiment, first dielectric layer 602 is composed of an oxide of thematerial of substrate 600. For example, in one embodiment, substrate 600is composed of silicon and first dielectric layer 602 is composed ofsilicon dioxide. In a specific embodiment, first dielectric layer 602 isformed to a thickness approximately in the range of 1-10 nanometers. Ina particular embodiment, first dielectric layer 602 is formed to athickness approximately in the range of 1.5-2.5 nanometers.

First dielectric layer 602 may be formed by a radical oxidation process.In accordance with an embodiment of the present invention, the radicaloxidation process involves flowing hydrogen (H₂) and oxygen (O₂) gasinto a furnace, such as the batch processing chamber 200 described inassociation with FIG. 2. In one embodiment, the partial pressures of H₂and O₂ have a ratio to one another of approximately 1:1. However, in anembodiment, an ignition event is not carried out which would otherwisetypically be used to pyrolyze the H₂ and O₂ to form steam. Instead, H₂and O₂ are permitted to react to form radicals at the surface ofsubstrate 600. In one embodiment, the radicals are used to consume thetop portion of substrate 600 to provide first dielectric layer 602. In aspecific embodiment, the radical oxidation process includes oxidizingwith a radical such as, but not limited to, an OH radical, an HO₂radical or an O diradical at a temperature approximately in the range of600-900 degrees Celsius. In a particular embodiment, the radicaloxidation process is carried out at a temperature approximately in therange of 700-800 degrees Celsius at a pressure approximately in therange of 0.5-5 Torr. In one embodiment, the radical oxidation process iscarried out for a duration approximately in the range of 100-150minutes. In accordance with an embodiment of the present invention,first dielectric layer 602 is formed as a high-density,low-hydrogen-content film.

Referring to operation 506 of Flowchart 500, subsequent to forming firstdielectric layer 602, but prior to any further processing, firstdielectric layer 602 may be subjected to a nitridation process. In anembodiment, the nitridation process is carried out in the same processchamber used to form first dielectric layer 502, without removingsubstrate 600 from the process chamber between process steps. In oneembodiment, the annealing includes heating substrate 600 in anatmosphere including nitrogen at a temperature approximately in therange of 700-800 degrees Celsius for a duration approximately in therange of 5 minutes-60 minutes. In one embodiment, the atmosphereincluding nitrogen is composed of a gas such as, but not limited to,nitrogen (N₂), nitrous oxide (N₂O), nitrogen dioxide (NO₂), nitric oxide(NO) or ammonia (NH₃). In one embodiment, the nitridation occursfollowing a nitrogen or argon purge of the process chamber following thefirst radical oxidation process. Alternatively, the above nitridationstep may be skipped.

FIG. 6C illustrates a cross-sectional view of a substrate having acharge-trapping layer formed thereon, corresponding to operation 508from the Flowchart of FIG. 5, in accordance with an embodiment of thepresent invention. Referring to operation 508 of Flowchart 500 andcorresponding FIG. 6C, a charge-trapping layer having a first region604A and a second region 604B is formed on first dielectric layer 602.In an embodiment, the formation of the charge-trapping layer is carriedout in the same process chamber used to form first dielectric layer 602,without removing substrate 600 from the process chamber between processsteps.

The charge-trapping layer may be composed of a material and have athickness suitable to store charge and, hence, change the thresholdvoltage of a subsequently formed gate stack. In accordance with anembodiment of the present invention, the charge-trapping layer iscomposed of two regions 604A and 604B, as depicted in FIG. 6C. In anembodiment, region 604A of the charge-trapping layer will remain as anintact charge-trapping layer following subsequent process operations.However, in that embodiment, region 604B of the as-formedcharge-trapping layer will be consumed to form a second dielectriclayer, above region 604A.

The charge-trapping layer having regions 604A and 604B may be formed bya chemical vapor deposition process. In accordance with an embodiment ofthe present invention, the charge-trapping layer is composed of amaterial such as, but not limited to, silicon nitride, siliconoxy-nitride, oxygen-rich silicon oxy-nitride or silicon-rich siliconoxy-nitride. In one embodiment, regions 604A and 604B of thecharge-trapping layer are formed at a temperature approximately in therange of 600-900 degrees Celsius. In a specific embodiment, thecharge-trapping layer is formed by using gases such as, but not limitedto, dichlorosilane (H₂SiCl₂), bis-(tert-butylamino)silane (BTBAS),ammonia (NH₃) or nitrous oxide (N₂O). In one embodiment, thecharge-trapping layer is formed to a total thickness approximately inthe range of 5-15 nanometers and region 604B accounts for a thicknessapproximately in the range of 2-3 nanometers of the total thickness ofthe charge-trapping layer. In that embodiment, region 604A accounts forthe remaining total thickness of the charge-trapping layer, i.e. region604A accounts for the portion of the charge-trapping layer that is notsubsequently consumed to form a top or blocking dielectric layer.

In another aspect of the present invention, the charge-trapping layermay include multiple composition regions. For example, in accordancewith an embodiment of the present invention, the charge-trapping layerincludes an oxygen-rich portion and a silicon-rich portion and is formedby depositing an oxygen-rich oxy-nitride film by a first composition ofgases and, subsequently, depositing a silicon-rich oxy-nitride film by asecond composition of gases. In one embodiment, the charge-trappinglayer is formed by modifying the flow rate of ammonia (NH₃) gas, andintroducing nitrous oxide (N₂O) and dichlorosilane (SiH₂Cl₂) to providethe desired gas ratios to yield first an oxygen-rich oxy-nitride filmand then a silicon-rich oxy-nitride film. In a specific embodiment, theoxygen-rich oxy-nitride film is formed by introducing a process gasmixture including N₂O, NH₃ and SiH₂Cl₂, while maintaining the processchamber at a pressure approximately in the range of 5-500 mTorr, andmaintaining substrate 600 at a temperature approximately in the range of700-850 degrees Celsius, for a period approximately in the range of2.5-20 minutes. In a further embodiment, the process gas mixtureincludes N₂O and NH₃ having a ratio of from about 8:1 to about 1:8 andSiH₂Cl₂ and NH₃ having a ratio of from about 1:7 to about 7:1, and canbe introduced at a flow rate approximately in the range of 5-200standard cubic centimeters per minute (sccm). In another specificembodiment, the silicon-rich oxy-nitride film is formed by introducing aprocess gas mixture including N₂O, NH₃ and SiH₂Cl₂, while maintainingthe chamber at a pressure approximately in the range of 5-500 mTorr, andmaintaining substrate 600 at a temperature approximately in the range of700-850 degrees Celsius, for a period approximately in the range of2.5-20 minutes. In a further embodiment, the process gas mixtureincludes N₂O and NH₃ having a ratio of from about 8:1 to about 1:8 andSiH₂Cl₂ and NH₃ mixed in a ratio of from about 1:7 to about 7:1,introduced at a flow rate of from about 5 to about 20 sccm. Inaccordance with an embodiment of the present invention, thecharge-trapping layer comprises a bottom oxygen-rich silicon oxy-nitrideportion having a thickness approximately in the range of 2.5-3.5nanometers and a top silicon-rich silicon oxy-nitride portion having athickness approximately in the range of 9-10 nanometers. In oneembodiment, a region 504B of charge-trapping layer accounts for athickness approximately in the range of 2-3 nanometers of the totalthickness of the top silicon-rich silicon oxy-nitride portion of thecharge-trapping layer. Thus, region 604B, which is targeted forsubsequent consumption to form a second dielectric layer, may becomposed entirely of silicon-rich silicon oxy-nitride.

FIG. 6D illustrates a cross-sectional view of a substrate having asecond dielectric layer formed thereon, corresponding to operation 510from the Flowchart of FIG. 5, in accordance with an embodiment of thepresent invention. Referring to operation 510 of Flowchart 500 andcorresponding FIG. 6D, a second dielectric layer 606 is formed oncharge-trapping layer 604. In an embodiment, the formation of seconddielectric layer 606 is carried out in the same process chamber used toform first dielectric layer 602 and the charge-trapping layer, withoutremoving substrate 600 from the process chamber between process steps.In one embodiment, the second radical oxidation process is carried outfollowing a nitrogen or argon purge of the process chamber following thedeposition of the charge-trapping layer.

Second dielectric layer 606 may be composed of a material and have athickness suitable to maintain a barrier to charge leakage withoutsignificantly decreasing the capacitance of a subsequently formed gatestack in a nonvolatile charge trap memory device. Second dielectriclayer 606 may be referred to in the art as a blocking dielectric layeror a top dielectric layer. In accordance with an embodiment of thepresent invention, second dielectric layer 606 is formed by consumingregion 604B of the charge-trapping layer formed in operation 508,described in association with FIG. 6C. Thus, in one embodiment, region604B is consumed to provide second dielectric layer 606, while region604A remains a charge-trapping layer 604. In a specific embodiment,region 604B is a silicon-rich silicon oxy-nitride region having athickness approximately in the range of 2-3 nanometers and is oxidizedto form second dielectric layer 606 having a thickness approximately inthe range of 3.5-4.5 nanometers. In that embodiment, second dielectriclayer 606 is composed of silicon dioxide. In accordance with anembodiment of the present invention, second dielectric layer 606 isformed by a second radical oxidation process, similar to the radicaloxidation process carried out to form blocking dielectric layer 406,described in association with FIG. 4B. In one embodiment, referring tooperation 512 of Flowchart 500, subsequent to forming second dielectriclayer 606, second dielectric layer 606 is further subjected to anitridation process similar to the nitridation process described inassociation with operation 506 from Flowchart 500. In a specificembodiment, the nitridation occurs following a nitrogen or argon purgeof the process chamber following the second radical oxidation process.Alternatively, this nitridation step may be skipped. In accordance withan embodiment of the present invention, no additional depositionprocesses are used in the formation of second dielectric layer 606.

Thus, in accordance with an embodiment of the present invention, an ONOstack including first dielectric layer 602, charge-trapping layer 604and second dielectric layer 606 is formed in a single pass in a processchamber. By fabricating these layers in a single pass of multiple wafersin the process chamber, high throughput requirements may be met whilestill ensuring the formation of very high quality films. Uponfabrication of an ONO stack including first dielectric layer 602,charge-trapping layer 604 and second dielectric layer 606, a nonvolatilecharge trap memory device may be fabricated to include a patternedportion of the ONO stack. FIG. 6E illustrates a cross-sectional view ofa nonvolatile charge trap memory device, in accordance with anembodiment of the present invention.

Referring to FIG. 6E, a nonvolatile charge trap memory device includes apatterned portion of the ONO stack formed over substrate 600. The ONOstack includes first dielectric layer 602, charge-trapping layer 604 andsecond dielectric layer 606. A gate layer 608 is disposed on seconddielectric layer 606. The nonvolatile charge trap memory device furtherincludes source and drain regions 612 in substrate 600 on either side ofthe ONO stack, defining a channel region 614 in substrate 600 underneaththe ONO stack. A pair of dielectric spacers 610 isolates the sidewallsof first dielectric layer 602, charge-trapping layer 604, seconddielectric layer 606 and gate layer 608. In a specific embodiment,channel region 614 is doped P-type and, in an alternative embodiment,channel region 614 is doped N-type.

In accordance with an embodiment of the present invention, thenonvolatile charge trap memory device described in association with FIG.6E is a SONOS-type device. By convention, SONOS stands for“Semiconductor-Oxide-Nitride-Oxide-Semiconductor,” where the first“Semiconductor” refers to the channel region material, the first “Oxide”refers to the tunnel dielectric layer, “Nitride” refers to thecharge-trapping dielectric layer, the second “Oxide” refers to the topdielectric layer (also known as a blocking dielectric layer) and thesecond “Semiconductor” refers to the gate layer. Thus, in accordancewith an embodiment of the present invention, first dielectric layer 602is a tunnel dielectric layer and second dielectric layer 606 is ablocking dielectric layer.

Gate layer 608 may be composed of any conductor or semiconductormaterial suitable for accommodating a bias during operation of aSONOS-type transistor. In accordance with an embodiment of the presentinvention, gate layer 608 is formed by a chemical vapor depositionprocess and is composed of doped poly-crystalline silicon. In anotherembodiment, gate layer 608 is formed by physical vapor deposition and iscomposed of a metal-containing material which may include, but is notlimited to, metal nitrides, metal carbides, metal silicides, hafnium,zirconium, titanium, tantalum, aluminum, ruthenium, palladium, platinum,cobalt or nickel.

Source and drain regions 612 in substrate 600 may be any regions havingopposite conductivity to channel region 614. For example, in accordancewith an embodiment of the present invention, source and drain regions612 are N-type doped regions while channel region 614 is a P-type dopedregion. In one embodiment, substrate 600 and, hence, channel region 614,is composed of boron-doped single-crystal silicon having a boronconcentration in the range of 1×10¹⁵-1×10¹⁹ atoms/cm³. In thatembodiment, source and drain regions 612 are composed of phosphorous- orarsenic-doped regions having a concentration of N-type dopants in therange of 5×10¹⁶-5×10¹⁹ atoms/cm³. In a specific embodiment, source anddrain regions 612 have a depth in substrate 600 in the range of 80-200nanometers. In accordance with an alternative embodiment of the presentinvention, source and drain regions 612 are P-type doped regions whilechannel region 614 is an N-type doped region.

In another aspect of the present invention, a dielectric layer formed byradical oxidation of the top surface of a substrate in an oxidationchamber may be less susceptible to crystal plane orientation differencesin the substrate upon which it is grown. For example, in one embodiment,the cornering effect caused by differential crystal plane oxidationrates is significantly reduced by forming a dielectric layer by aradical oxidation process. FIG. 7A illustrates a cross-sectional view ofa substrate including first and second exposed crystal planes, inaccordance with an embodiment of the present invention.

Referring to FIG. 7A, a substrate 700 has isolation regions 702 formedthereon. Substrate 700 may be composed of a material described inassociation with substrate 600 from FIG. 6A. Isolation regions 702 maybe composed of an insulating material suitable for adhesion to substrate700. An exposed portion of substrate 700 extends above the top surfaceof isolation regions 702. In accordance with an embodiment of thepresent invention, the exposed portion of substrate 700 has a firstexposed crystal plane 704 and a second exposed crystal plane 706. In oneembodiment, the crystal orientation of first exposed crystal plane 704is different from the crystal orientation of second exposed crystalplane 706. In a specific embodiment, substrate 700 is composed ofsilicon, first exposed crystal plane 704 has <100> orientation, andsecond exposed crystal plane 706 has <110> orientation.

Substrate 700 may be subjected to a radical oxidation process to form adielectric layer by consuming (oxidizing) the top surface of substrate700. In one embodiment, the oxidizing of substrate 700 by a radicaloxidation process includes oxidizing with a radical selected from thegroup consisting of an OH radical, an HO₂ radical or an O diradical.FIG. 7B illustrates a cross-sectional view of substrate 700 includingfirst and second crystal planes 704 and 706, respectively, and having adielectric layer 708 formed thereon, in accordance with an embodiment ofthe present invention. In an embodiment, first portion 708A ofdielectric layer 708 is formed on first exposed crystal plane 704 and asecond portion 708B of dielectric layer 708 is formed on second exposedcrystal plane 706, as depicted in FIG. 7B. In one embodiment, thethickness T1 of first portion 708A of dielectric layer 708 isapproximately equal to the thickness T2 of second portion 708B ofdielectric layer 708, even though the crystal plane orientation of firstexposed crystal plane 704 and second exposed crystal plane 706 differ.In a specific embodiment, the radical oxidation of substrate 700 iscarried out at a temperature approximately in the range of 600-900degrees Celsius. In a specific embodiment, the radical oxidation ofsubstrate 700 is carried out at a temperature approximately in the rangeof 700-800 degrees Celsius at a pressure approximately in the range of0.5-5 Torr.

Thus, a method for fabricating a nonvolatile charge trap memory devicehas been disclosed. In accordance with an embodiment of the presentinvention, a substrate is provided having a charge-trapping layerdisposed thereon. A portion of the charge-trapping layer is thenoxidized to form a blocking dielectric layer above the charge-trappinglayer by exposing the charge-trapping layer to a radical oxidationprocess.

In another aspect of the present invention, it may be desirable to use acluster tool to carry out a radical oxidation process. Accordingly,disclosed herein is a method to fabricate a nonvolatile charge trapmemory device. A substrate may first be subjected to a first radicaloxidation process to form a first dielectric layer in a first processchamber of a cluster tool. In one embodiment, a charge-trapping layer isthen deposited above the first dielectric layer in a second processchamber of the cluster tool. The charge-trapping layer may then besubjected to a second radical oxidation process to form a seconddielectric layer above the charge-trapping layer. In one embodiment, thesecond dielectric layer is formed by oxidizing a portion of thecharge-trapping layer in the first process chamber of the cluster tool.In a specific embodiment, the cluster tool is a single-wafer clustertool.

Formation of a dielectric layer in a chamber of a cluster tool maypermit the growth of the dielectric layer at temperatures higher thannormally achievable in batch processing chambers. Furthermore, a radicaloxidation process may be carried out in the chamber of the cluster toolas the primary pathway for growing the dielectric layer. In accordancewith an embodiment of the present invention, a radical oxidation processinvolving flowing hydrogen (H₂) and oxygen (O₂) gas into an oxidationchamber of a cluster tool is carried out to effect growth of adielectric layer by oxidation consumption of an exposed substrate orfilm. In one embodiment, multiple radical oxidation processes arecarried out in an oxidation chamber of a cluster tool to provide atunnel dielectric layer and a blocking dielectric layer for anon-volatile charge trap memory device. These dielectric layers may beof very high quality, even at a reduced thickness. In one embodiment,the tunnel dielectric layer and the blocking dielectric layer are bothdenser and are composed of substantially fewer hydrogen atoms/cm³ than atunnel dielectric layer or a blocking dielectric layer formed in a batchprocess chamber. Furthermore, the substrate upon which a tunneldielectric layer and a blocking dielectric layer are formed may beexposed to a shorter temperature ramp rate and stabilization time in anoxidation chamber of a cluster tool as compared with a batch processchamber. Thus, in accordance with an embodiment of the present inventionembodiment, the impact on the thermal budget of the substrate is reducedby employing a radical oxidation process in an oxidation chamber of acluster tool. In accordance with another embodiment of the presentinvention, a dielectric layer formed by carrying out a radical oxidationprocess in an oxidation chamber of a cluster tool is less susceptible tocrystal plane orientation differences in the substrate from which it isgrown. In one embodiment, the cornering effect caused by differentialcrystal plane oxidation rates is significantly reduced by forming adielectric layer via a radical oxidation process carried out in anoxidation chamber of a cluster tool.

A portion of a nonvolatile charge trap memory device may be fabricatedin a cluster tool. FIG. 8 illustrates an arrangement of process chambersin a cluster tool, in accordance with an embodiment of the presentinvention. Referring to FIG. 8, an arrangement of process chambers in acluster tool 800 includes a transfer chamber 802, a first processchamber 804, a second process chamber 806 and a third process chamber808. In an embodiment, transfer chamber 802 is for receiving a waferfrom an external environment for introduction into cluster tool 800. Inone embodiment, each of the process chambers 802, 804 and 806 arearranged in a way such that a wafer may be passed back- and forthbetween these chambers and transfer chamber 802, as depicted by thedouble-headed arrows in FIG. 8. In accordance with an additionalembodiment of the present invention, although not shown, cluster tool800 may be configured such that a wafer can be transferred directlybetween any pairing of process chambers 802, 804 or 806.

Cluster tool 800 may be any cluster tool for which an outsideenvironment is excluded in and between process chambers 804, 806 and 808and transfer chamber 802. Thus, in accordance with an embodiment of thepresent invention, once a wafer has entered process chamber 802, it isprotected from an external environment as it is moved into and betweenprocess chambers 804, 806 and 808 and transfer chamber 802. An exampleof such a cluster tool is the Centura® platform commercially availablefrom Applied Materials, Inc., located in Santa Clara, Calif. In oneembodiment, once a wafer has been received by transfer chamber 802, avacuum of less than approximately 100 mTorr is maintained in clustertool 800. In accordance with an embodiment of the present invention,cluster tool 800 incorporates a chuck (or multiple chucks, e.g., onechuck for each chamber) upon which the flat surface, as opposed to theedge surface, of a wafer rests on the chuck for processing and transferevents. In one embodiment, by having the flat surface of a wafer rest onthe chuck, more rapid ramp rates for heating the wafer are achievable byheating the wafer via the chuck. In a specific embodiment, cluster tool800 is a single-wafer cluster tool.

Process chambers 802, 804 and 806 may include, but are not limited to,oxidation chambers, low-pressure chemical vapor deposition chambers, ora combination thereof. For example, in accordance with an embodiment ofthe present invention, first process chamber 804 is a first oxidationchamber, second process chamber 806 is a low-pressure chemical vapordeposition chamber, and third process chamber 808 is a second oxidationchamber. An example of an oxidation chamber is the In-Situ SteamGeneration (ISSG) chamber from Applied Materials, Inc. Examples oflow-pressure chemical vapor deposition chambers include a SiNgen™chamber and an OXYgen™ chamber from Applied Materials, Inc. Instead ofheating entire process chambers to heat a wafer, which is the case fortypical batch process chambers, a chuck used for carrying a single wafermay be heated to heat the wafer. In accordance with an embodiment of thepresent invention, a chuck is used to heat a wafer to the desiredprocess temperature. Thus, relatively short temperature ramp times andstabilization times may be achieved.

A portion of a nonvolatile charge trap memory device may be fabricatedin a cluster tool. FIG. 9 depicts a Flowchart 900 representing a seriesof operations in a method for fabricating a nonvolatile charge trapmemory device, in accordance with an embodiment of the presentinvention. FIGS. 10A-10E illustrate cross-sectional views representingoperations in the fabrication of a nonvolatile charge trap memorydevice, in accordance with an embodiment of the present invention.

Referring to FIG. 10A, a substrate 1000 is provided in a cluster tool.In one embodiment, substrate 1000 is provided in a transfer chamber,such as transfer chamber 802 described in association with FIG. 8.

Substrate 1000 may be composed of any material suitable forsemiconductor device fabrication. In one embodiment, substrate 1000 is abulk substrate composed of a single crystal of a material which mayinclude, but is not limited to, silicon, germanium, silicon-germanium ora III-V compound semiconductor material. In another embodiment,substrate 1000 includes a bulk layer with a top epitaxial layer. In aspecific embodiment, the bulk layer is composed of a single crystal of amaterial which may include, but is not limited to, silicon, germanium,silicon-germanium, a III-V compound semiconductor material or quartz,while the top epitaxial layer is composed of a single crystal layerwhich may include, but is not limited to, silicon, germanium,silicon-germanium or a III-V compound semiconductor material. In anotherembodiment, substrate 1000 includes a top epitaxial layer on a middleinsulator layer which is above a lower bulk layer. The top epitaxiallayer is composed of a single crystal layer which may include, but isnot limited to, silicon (i.e. to form a silicon-on-insulator (SOI)semiconductor substrate), germanium, silicon-germanium or a III-Vcompound semiconductor material. The insulator layer is composed of amaterial which may include, but is not limited to, silicon dioxide,silicon nitride or silicon oxy-nitride. The lower bulk layer is composedof a single crystal which may include, but is not limited to, silicon,germanium, silicon-germanium, a III-V compound semiconductor material orquartz. Substrate 1000 may further include dopant impurity atoms.

FIG. 10B illustrates a cross-sectional view of a substrate having atunnel dielectric layer formed thereon, corresponding to operation 902from the Flowchart of FIG. 9, in accordance with an embodiment of thepresent invention. Referring to operation 902 of Flowchart 900 andcorresponding FIG. 10B, substrate 1000 is subjected to a first radicaloxidation process in a first process chamber of the cluster tool to forma first dielectric layer 1002.

First dielectric layer 1002 may be composed of a material and have athickness suitable to allow charge carriers to tunnel into asubsequently formed charge-trapping layer under an applied gate bias,while maintaining a suitable barrier to leakage when a subsequentlyformed nonvolatile charge trap memory device is unbiased. In accordancewith an embodiment of the present invention, first dielectric layer 1002is formed by an oxidation process where the top surface of substrate1000 is consumed. Thus, in an embodiment, first dielectric layer 1002 iscomposed of an oxide of the material of substrate 1000. For example, inone embodiment, substrate 1000 is composed of silicon and firstdielectric layer 1002 is composed of silicon dioxide. In a specificembodiment, first dielectric layer 1002 is formed to a thicknessapproximately in the range of 1-10 nanometers. In a particularembodiment, first dielectric layer 1002 is formed to a thicknessapproximately in the range of 1.5-2.5 nanometers.

First dielectric layer 1002 may be formed by a radical oxidationprocess. In accordance with an embodiment of the present invention, theradical oxidation process involves flowing hydrogen (H₂) and oxygen (O₂)gas into an oxidation chamber, such as the oxidation chambers 804 or 808described in association with FIG. 8. In one embodiment, the partialpressures of H₂ and O₂ have a ratio to one another approximately in therange of 1:50-1:5. However, in an embodiment, an ignition event is notcarried out which would otherwise typically be used to pyrolyze the H₂and O₂ to form steam. Instead, H₂ and O₂ are permitted to react to formradicals at the surface of substrate 1000. In one embodiment, theradicals are used to consume the top portion of substrate 1000 toprovide first dielectric layer 1002. In a specific embodiment, theradical oxidation process includes oxidizing with a radical such as, butnot limited to, an OH radical, an HO₂ radical or an O diradical. In aparticular embodiment, the radical oxidation process is carried out at atemperature approximately in the range of 950-1100 degrees Celsius at apressure approximately in the range of 5-15 Torr. In one embodiment, theradical oxidation process is carried out for a duration approximately inthe range of 1-3 minutes. In accordance with an embodiment of thepresent invention, first dielectric layer 1002 is formed as ahigh-density, low-hydrogen-content film.

Referring to operation 904 of Flowchart 900, subsequent to forming firstdielectric layer 1002, but prior to any further processing, firstdielectric layer 1002 may be subjected to a nitridation process. In anembodiment, the nitridation process is carried out in the same processchamber used to form first dielectric layer 1002. In one embodiment,first dielectric layer 1002 is annealed in the first process chamber,wherein the annealing includes heating substrate 1000 in an atmosphereincluding nitrogen at a temperature approximately in the range of900-1100 degrees Celsius for a duration approximately in the range of 30seconds-60 seconds. In one embodiment, the atmosphere including nitrogenis composed of a gas such as, but not limited to, nitrogen (N₂), nitrousoxide (N₂O), nitrogen dioxide (NO₂), nitric oxide (NO) or ammonia (NH₃).In another embodiment, the nitridation occurs in a separate processchamber. Alternatively, this nitridation step may be skipped.

FIG. 10C illustrates a cross-sectional view of a substrate having acharge-trapping layer formed thereon, corresponding to operation 906from the Flowchart of FIG. 9, in accordance with an embodiment of thepresent invention. Referring to operation 906 of Flowchart 900 andcorresponding FIG. 10C, a charge-trapping layer having a first region1004A and a second region 1004B is formed on first dielectric layer 1002in the second process chamber of a cluster tool.

The charge-trapping layer may be composed of a material and have athickness suitable to store charge and, hence, change the thresholdvoltage of a subsequently formed gate stack. In accordance with anembodiment of the present invention, the charge-trapping layer iscomposed of two regions 1004A and 1004B, as depicted in FIG. 10C. In anembodiment, region 1004A of the charge-trapping layer will remain as anintact charge-trapping layer following subsequent process operations.However, in that embodiment, region 1004B of the as-formedcharge-trapping layer will be consumed to form a second dielectriclayer, above region 1004A. In one embodiment, regions 1004A and 1004B ofthe charge-trapping layer are formed in the same process step and arecomposed of the same material.

The charge-trapping layer having regions 1004A and 1004B may be formedby a chemical vapor deposition process. In accordance with an embodimentof the present invention, the charge-trapping layer is composed of amaterial such as, but not limited to, silicon nitride, siliconoxy-nitride, oxygen-rich silicon oxy-nitride or silicon-rich siliconoxy-nitride. In an embodiment, the charge-trapping layer is formed onfirst dielectric layer 1002 in a low-pressure chemical vapor depositionchamber, such as the SiNgen™ low-pressure chemical vapor depositionchamber described in association with process chamber 806 from FIG. 8.In one embodiment, the second process chamber is a low-pressure chemicalvapor deposition chamber and regions 1004A and 1004B of thecharge-trapping layer are formed at a temperature less than thetemperature used to form first dielectric layer 1002. In a specificembodiment, regions 1004A and 1004B of the charge-trapping layer areformed at a temperature approximately in the range of 700-850 degreesCelsius. In an embodiment, the second process chamber is a low-pressurechemical vapor deposition chamber and the charge-trapping layer isformed by using gases such as, but not limited to, dichlorosilane(H₂SiCl₂), bis-(tert-butylamino)silane (BTBAS), ammonia (NH₃) or nitrousoxide (N₂O). In accordance with an embodiment of the present invention,the charge-trapping layer is formed to a total thickness approximatelyin the range of 5-15 nanometers and region 1004B accounts for athickness approximately in the range of 2-3 nanometers of the totalthickness of the charge-trapping layer. In that embodiment, region 1004Aaccounts for the remaining total thickness of the charge-trapping layer,i.e. the portion of the charge-trapping layer that is not subsequentlyconsumed to form a top or blocking dielectric layer.

In another aspect of the present invention, the charge-trapping layermay include multiple composition regions. For example, in accordancewith an embodiment of the present invention, the charge-trapping layerincludes an oxygen-rich portion and a silicon-rich portion and is formedby depositing an oxygen-rich oxy-nitride film by a first composition ofgases in the second process chamber and, subsequently, depositing asilicon-rich oxy-nitride film by a second composition of gases in thesecond process chamber. In one embodiment, the charge-trapping layer isformed by modifying the flow rate of ammonia (NH₃) gas, and introducingnitrous oxide (N₂O) and dichlorosilane (SiH₂Cl₂) to provide the desiredgas ratios to yield first an oxygen-rich oxy-nitride film and then asilicon-rich oxy-nitride film. In a specific embodiment, the oxygen-richoxy-nitride film is formed by introducing a process gas mixtureincluding N₂O, NH₃ and SiH₂Cl₂, while maintaining the chamber at apressure approximately in the range of 0.5-500 Torr, and maintainingsubstrate 1000 at a temperature approximately in the range of 700-850degrees Celsius, for a period approximately in the range of 2.5-20minutes. In a further embodiment, the process gas mixture includes N₂Oand NH₃ having a ratio of from about 8:1 to about 1:8 and SiH₂Cl₂ andNH₃ having a ratio of from about 1:7 to about 7:1, and can be introducedat a flow rate approximately in the range of 5-200 standard cubiccentimeters per minute (sccm). In another specific embodiment, thesilicon-rich oxy-nitride film is formed by introducing a process gasmixture including N₂O, NH₃ and SiH₂Cl₂, while maintaining the chamber ata pressure approximately in the range of 0.5-500 Torr, and maintainingsubstrate 1000 at a temperature approximately in the range of 700-850degrees Celsius, for a period approximately in the range of 2.5-20minutes. In a further embodiment, the process gas mixture includes N₂Oand NH₃ having a ratio of from about 8:1 to about 1:8 and SiH₂Cl₂ andNH₃ mixed in a ratio of from about 1:7 to about 7:1, introduced at aflow rate of from about 5 to about 20 sccm. In accordance with anembodiment of the present invention, the charge-trapping layer comprisesa bottom oxygen-rich silicon oxy-nitride portion having a thicknessapproximately in the range of 2.5-3.5 nanometers and a top silicon-richsilicon oxy-nitride portion having a thickness approximately in therange of 9-10 nanometers. In one embodiment, a region 1004B ofcharge-trapping layer accounts for a thickness approximately in therange of 2-3 nanometers of the total thickness of the top silicon-richsilicon oxy-nitride portion of the charge-trapping layer. Thus, region1004B, which is targeted for subsequent consumption to form a seconddielectric layer, may be composed entirely of silicon-rich siliconoxy-nitride.

FIG. 10D illustrates a cross-sectional view of a substrate having a topdielectric layer formed thereon, corresponding to operation 908 from theFlowchart of FIG. 9, in accordance with an embodiment of the presentinvention. Referring to operation 908 of Flowchart 900 and correspondingFIG. 10D, a second dielectric layer 1006 is formed on charge-trappinglayer 1004 in the first process chamber of the cluster tool.

Second dielectric layer 1006 may be composed of a material and have athickness suitable to maintain a barrier to charge leakage withoutsignificantly decreasing the capacitance of a subsequently formed gatestack in a nonvolatile charge trap memory device. In accordance with anembodiment of the present invention, second dielectric layer 1006 isformed by consuming region 1004B of the charge trapping layer formed inoperation 906, described in association with FIG. 10C. Thus, in oneembodiment region 1004B is consumed to provide second dielectric layer1006, while region 1004A remains a charge-trapping layer 1004. In aspecific embodiment, region 1004B is a silicon-rich silicon oxy-nitrideregion having a thickness approximately in the range of 2-3 nanometersand is oxidized to form second dielectric layer 1006 having a thicknessapproximately in the range of 3.5-4.5 nanometers. In that embodiment,second dielectric layer 1006 is composed of silicon dioxide.

Second dielectric layer 1006 may be formed by a second radical oxidationprocess. In accordance with an embodiment of the present invention, thesecond radical oxidation process involves flowing hydrogen (H₂) andoxygen (O₂) gas into an oxidation chamber, such as the oxidationchambers 804 or 808 described in association with FIG. 8. In oneembodiment, the partial pressures of H₂ and O₂ have a ratio to oneanother approximately in the range of 1:50-1:5. However, in anembodiment, an ignition event is not carried out which would otherwisetypically be used to pyrolyze the H₂ and O₂ to form steam. Instead, H₂and O₂ are permitted to react to form radicals at the surface of region1004B. In one embodiment, the radicals are used to consume region 1004Bto provide second dielectric layer 1006. In a specific embodiment, thesecond radical oxidation process includes oxidizing with a radical suchas, but not limited to, an OH radical, an HO₂ radical or an O diradical.In a particular embodiment, the second radical oxidation process iscarried out at a temperature approximately in the range of 950-1100degrees Celsius at a pressure approximately in the range of 5-15 Torr.In one embodiment, the second radical oxidation process is carried outfor a duration approximately in the range of 1-3 minutes. In accordancewith an embodiment of the present invention, first dielectric layer 1002is formed as a high-density, low-hydrogen-content film. In oneembodiment, no additional deposition step is required to form a completesecond dielectric layer 1006, as depicted in FIG. 10D and shown inFlowchart 900. Depending on wafer pass-through logistics in the clustertool, the second radical oxidation process may be carried out in thesame, i.e. first, chamber as the first radical oxidation process used toform first dielectric layer 1002 or in a different, e.g. third, processchamber of the cluster tool. Thus, in accordance with an embodiment ofthe present invention, reference to a first process chamber can be usedto mean reintroduction into the first process chamber or to meanintroduction into a process chamber different from the first processchamber.

Referring to operation 910 of Flowchart 900, subsequent to formingsecond dielectric layer 1006, but prior to removing substrate 1000 fromthe cluster tool, second dielectric layer 1006 may be further subjectedto a nitridation process in the first process chamber. In accordancewith an embodiment of the present invention, the nitridation processincludes annealing second dielectric layer 1006 in an atmosphereincluding nitrogen at a temperature approximately in the range of900-1100 degrees Celsius for a duration approximately in the range of 30seconds-60 seconds. In one embodiment, the atmosphere including nitrogenis composed of a gas such as, but not limited to, nitrogen (N₂), nitrousoxide (N₂O), nitrogen dioxide (NO₂), nitric oxide (NO) or ammonia (NH₃).Alternatively, this nitridation step, i.e. operation 910 from Flowchart900, may be skipped and the wafer unloaded from the cluster tool.

Thus, in accordance with an embodiment of the present invention, an ONOstack including first dielectric layer 1002, charge-trapping layer 1004and second dielectric layer 1006 is formed in a single pass in a clustertool. By fabricating these layers in a single pass in the cluster tool,pristine interfaces between first dielectric layer 1002 andcharge-trapping layer 1004 and between charge-trapping layer 1004 andsecond dielectric layer 1006 may be preserved. In one embodiment, firstdielectric layer 1002, charge-trapping layer 1004 and second dielectriclayer 1006 are formed without breaking vacuum in the cluster tool. Inone embodiment, each layer is formed at a different temperature totailor film properties without incurring significant ramp timepenalties. Furthermore, by fabricating these layers in a cluster tool,as opposed to fabricating in batch processing tools, the overalluniformity of the stack of layers may be optimized. For example, inaccordance with an embodiment of the present invention, by fabricatinglayers 1002, 1004 and 1006 in a cluster tool, the variability inthickness of the stack of layers 1002, 1004 and 1006 across a singlewafer may be reduced by as much as approximately 30%. In an exemplaryembodiment, 1 σ is approximately in the range of 1-2% of the thicknessof first dielectric layer 1002. In a specific embodiment, the clustertool is a single-wafer cluster tool.

Upon fabrication of an ONO stack including first dielectric layer 1002,charge-trapping layer 1004 and second dielectric layer 1006, anonvolatile charge trap memory device may be fabricated to include apatterned portion of the ONO stack. FIG. 10E illustrates across-sectional view of a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

Referring to FIG. 10E, a nonvolatile charge trap memory device includesa patterned portion of the ONO stack formed over substrate 1000. The ONOstack includes first dielectric layer 1002, charge-trapping layer 1004and second dielectric layer 1006. A gate layer 1008 is disposed onsecond dielectric layer 1006. The nonvolatile charge trap memory devicefurther includes source and drain regions 1012 in substrate 1000 oneither side of the ONO stack, defining a channel region 1014 insubstrate 1000 underneath the ONO stack. A pair of dielectric spacers1010 isolates the sidewalls of first dielectric layer 1002,charge-trapping layer 1004, second dielectric layer 1006 and gate layer1008. In a specific embodiment, channel region 1014 is doped P-type and,in an alternative embodiment, channel region 1014 is doped N-type.

In accordance with an embodiment of the present invention, thenonvolatile charge trap memory device described in association with FIG.10E is a SONOS-type device. By convention, SONOS stands for“Semiconductor-Oxide-Nitride-Oxide-Semiconductor,” where the first“Semiconductor” refers to the channel region material, the first “Oxide”refers to the tunnel dielectric layer, “Nitride” refers to thecharge-trapping dielectric layer, the second “Oxide” refers to the topdielectric layer (also known as a blocking dielectric layer) and thesecond “Semiconductor” refers to the gate layer. Thus, in accordancewith an embodiment of the present invention, first dielectric layer 1002is a tunnel dielectric layer and second dielectric layer 1006 is ablocking dielectric layer.

Gate layer 1008 may be composed of any conductor or semiconductormaterial suitable for accommodating a bias during operation of aSONOS-type transistor. In accordance with an embodiment of the presentinvention, gate layer 1008 is formed by a chemical vapor depositionprocess and is composed of doped poly-crystalline silicon. In anotherembodiment, gate layer 1008 is formed by physical vapor deposition andis composed of a metal-containing material which may include, but is notlimited to, metal nitrides, metal carbides, metal silicides, hafnium,zirconium, titanium, tantalum, aluminum, ruthenium, palladium, platinum,cobalt or nickel.

Source and drain regions 1012 in substrate 1000 may be any regionshaving opposite conductivity to channel region 1014. For example, inaccordance with an embodiment of the present invention, source and drainregions 1012 are N-type doped regions while channel region 1014 is aP-type doped region. In one embodiment, substrate 1000 and, hence,channel region 1014, is composed of boron-doped single-crystal siliconhaving a boron concentration in the range of 1×10¹⁵-1-10¹⁹ atoms/cm³. Inthat embodiment, source and drain regions 1012 are composed ofphosphorous- or arsenic-doped regions having a concentration of N-typedopants in the range of 5×10¹⁶-5×10¹⁹ atoms/cm³. In a specificembodiment, source and drain regions 1012 have a depth in substrate 1000in the range of 80-200 nanometers. In accordance with an alternativeembodiment of the present invention, source and drain regions 1012 areP-type doped regions while channel region 1014 is an N-type dopedregion.

In another aspect of the present invention, a charge-trapping layer mayinclude multiple composition regions, where the composition regionclosest to a tunnel dielectric layer is subjected to a radical oxidationprocess. FIG. 11 depicts a Flowchart 1100 representing a series ofoperations in a method for fabricating a nonvolatile charge trap memorydevice, in accordance with an embodiment of the present invention. FIGS.12A-12E illustrate cross-sectional views representing operations in thefabrication of a nonvolatile charge trap memory device, in accordancewith an embodiment of the present invention.

FIG. 12A illustrates a cross-sectional view of a substrate having afirst dielectric layer formed thereon, corresponding to operation 1102from the Flowchart of FIG. 11, in accordance with an embodiment of thepresent invention. Referring to operation 1102 of Flowchart 1100 andcorresponding FIG. 12A, substrate 1200 is subjected to a first radicaloxidation process in a first process chamber of a cluster tool to form afirst dielectric layer 1202. Substrate 1200 and first dielectric layer1202 may be composed of materials described in association withsubstrate 1000 and first dielectric layer 1002 from FIGS. 10A and 10B,respectively. The radical oxidation process used to form firstdielectric layer 1202 may be similar to the radical oxidation processused to form first dielectric layer 1002, described in association withFIG. 10B.

Referring to operation 1104 of Flowchart 1100, subsequent to formingfirst dielectric layer 1202, but prior to any further processing, firstdielectric layer 1202 may be subjected to a nitridation process. Thenitridation process may be similar to the nitridation process describedin association with operation 904 of Flowchart 900. In one embodiment,the nitridation process is carried out in the same process chamber usedto form first dielectric layer 1202. In another embodiment, thenitridation occurs in a separate process chamber. Alternatively, thisnitridation step may be skipped.

FIG. 12B illustrates a cross-sectional view of a substrate having anoxygen-rich silicon oxy-nitride portion of a charge-trapping layerformed thereon, corresponding to operation 1106 from the Flowchart ofFIG. 11, in accordance with an embodiment of the present invention.Referring to operation 1106 of Flowchart 1100 and corresponding FIG.12B, an oxygen-rich silicon oxy-nitride portion 1204A is formed on firstdielectric layer 1202 in a second process chamber of the cluster tool.Oxygen-rich silicon oxy-nitride portion 1204A may be composed of anoxygen-rich silicon oxy-nitride material and formed by a techniquedescribed in association with first region 1004A from FIG. 10C.

Referring to operation 1108 from Flowchart 1100, in accordance with anembodiment of the present invention, oxygen-rich silicon oxy-nitrideportion 1204A is subjected to a second radical oxidation process in thefirst process chamber of the cluster tool. The second radical oxidationprocess may be similar to one of the radical oxidation processes used toform first dielectric layer 1002 or second dielectric layer 1006,described in association with FIGS. 10B and 10D, respectively. In anembodiment, carrying out the second radical oxidation process is madepossible because oxygen-rich silicon oxy-nitride portion 1204A ismaintained in the environment within the tool and thus retains apristine surface. In one embodiment, the second radical oxidationprocess densifies oxygen-rich silicon oxy-nitride portion 1204A.Depending on wafer pass-through logistics in the cluster tool, thesecond radical oxidation process may be carried out in the same, i.e.first, chamber as the radical oxidation process used to form firstdielectric layer 1202 or in a different, e.g. third, process chamber.Thus, in accordance with an embodiment of the present invention,reference to a first process chamber can be used to mean reintroductioninto the first process chamber or to mean introduction into a processchamber different from the first process chamber.

FIG. 12C illustrates a cross-sectional view of a substrate having asilicon-rich silicon oxy-nitride portion of a charge-trapping layerformed thereon, corresponding to operation 1110 from the Flowchart ofFIG. 11, in accordance with an embodiment of the present invention.Referring to operation 1110 of Flowchart 1100 and corresponding FIG.12C, a silicon-rich silicon oxy-nitride portion having a first region1204B and a second region 1204C is formed on oxygen-rich siliconoxy-nitride portion 1204A in the second process chamber of the clustertool. The silicon-rich silicon oxy-nitride portion may be composed of asilicon-rich silicon oxy-nitride material and formed by a techniquedescribed in association with second region 1004B from FIG. 10C.Depending on wafer pass-through logistics in the cluster tool, thedeposition of silicon-rich silicon oxy-nitride portion of thecharge-trapping layer may be carried out in the same, i.e. second,chamber as the deposition of oxygen-rich silicon oxy-nitride portion1204A of the charge-trapping layer or in a different process chamber.Thus, in accordance with an embodiment of the present invention,reference to a second process chamber can be used to mean reintroductioninto the second process chamber or to mean introduction into a processchamber different from the second process chamber.

FIG. 12D illustrates a cross-sectional view of a substrate having a topdielectric layer formed thereon, corresponding to operation 1112 fromthe Flowchart of FIG. 11, in accordance with an embodiment of thepresent invention. Referring to operation 1112 of Flowchart 1100 andcorresponding FIG. 12D, a second dielectric layer 1206 is formed oncharge-trapping layer 1204 in the first process chamber of the clustertool. In accordance with an embodiment of the present invention, seconddielectric layer 1206 is formed by consuming second region 1204C of thesilicon-rich silicon oxy-nitride portion by a third radical oxidationprocess. Thus, in one embodiment, the remaining charge-trapping layer1204 between first dielectric layer 1202 and second dielectric layer1204 is composed of oxygen-rich silicon oxy-nitride portion 1204A andfirst region 1204B of the silicon-rich silicon oxy-nitride portion 1204,as depicted in FIG. 12D. The third radical oxidation process used toconsume second region 1204C of the silicon-rich silicon oxy-nitrideportion to provide second dielectric layer 1206 may be similar to theradical oxidation process used to form second dielectric layer 1006,described in association with FIG. 10D. Depending on wafer pass-throughlogistics in the cluster tool, the third radical oxidation process maybe carried out in the same, i.e. first, chamber as the radical oxidationprocess used to form first dielectric layer 1202 or in a different, e.g.third, process chamber. Thus, in accordance with an embodiment of thepresent invention, reference to a first process chamber can be used tomean reintroduction into the first process chamber or to meanintroduction into a process chamber different from the first processchamber.

Referring to operation 1114 of Flowchart 1100, subsequent to formingsecond dielectric layer 1206, but prior to removing substrate 1200 fromthe cluster tool, second dielectric layer 1206 may be further subjectedto a nitridation process in the first process chamber. The nitridationprocess may be similar to the nitridation process described inassociation with operation 910 from Flowchart 900. In one embodiment,the nitridation process is carried out in the same process chamber usedto form second dielectric layer 1206. In another embodiment, thenitridation occurs in a separate process chamber. Alternatively, thisnitridation step may be skipped.

Upon fabrication of an ONO stack including first dielectric layer 1202,charge-trapping layer 1204 and second dielectric layer 1206, anonvolatile charge trap memory device may be fabricated to include apatterned portion of the ONO stack. FIG. 12E illustrates across-sectional view of a nonvolatile charge trap memory device, inaccordance with an embodiment of the present invention.

Referring to FIG. 12E, a nonvolatile charge trap memory device includesa patterned portion of the ONO stack formed over substrate 1200. The ONOstack includes first dielectric layer 1202, charge-trapping layer 1204and second dielectric layer 1206. A gate layer 1208 is disposed onsecond dielectric layer 1206. The nonvolatile charge trap memory devicefurther includes source and drain regions 1212 in substrate 1200 oneither side of the ONO stack, defining a channel region 1214 insubstrate 1200 underneath the ONO stack. A pair of dielectric spacers1210 isolates the sidewalls of first dielectric layer 1202,charge-trapping layer 1204, second dielectric layer 1206 and gate layer1208. In accordance with an embodiment of the present invention,charge-trapping layer 1204 is composed of an oxygen-rich siliconoxy-nitride portion 1204A and a silicon-rich silicon oxy-nitride portion1204B, as depicted in FIG. 12E. In one embodiment, the nonvolatilecharge trap memory device is a SONOS-type device. Gate layer 1208,source and drain regions 1212 and channel region 1214 may be composed ofmaterials described in association with gate layer 1008, source anddrain regions 1012 and channel region 1014 from FIG. 10E.

In another aspect of the present invention, a dielectric layer formed byradical oxidation of the top surface of a substrate in an oxidationchamber may be less susceptible to crystal plane orientation differencesin the substrate upon which it is grown. For example, in one embodiment,the cornering effect caused by differential crystal plane oxidationrates is significantly reduced by forming a dielectric layer in anoxidation chamber of a cluster tool. FIG. 13A illustrates across-sectional view of a substrate including first and second exposedcrystal planes, in accordance with an embodiment of the presentinvention.

Referring to FIG. 13A, a substrate 1300 has isolation regions 1302formed thereon. Substrate 1300 may be composed of a material describedin association with substrate 1000 from FIG. 10A. Isolation regions 1302may be composed of an insulating material suitable for adhesion tosubstrate 1300. An exposed portion of substrate 1300 extends above thetop surface of isolation regions 1302. In accordance with an embodimentof the present invention, the exposed portion of substrate 1300 has afirst exposed crystal plane 1304 and a second exposed crystal plane1306. In one embodiment, the crystal orientation of first exposedcrystal plane 1304 is different from the crystal orientation of secondexposed crystal plane 1306. In a specific embodiment, substrate 1300 iscomposed of silicon, first exposed crystal plane 1304 has <100>orientation, and second exposed crystal plane 1306 has <110>orientation.

Substrate 1300 may be subjected to a radical oxidation process in acluster tool to form a dielectric layer by consuming (oxidizing) the topsurface of substrate 1300. In one embodiment, the oxidizing of substrate1300 by a radical oxidation process includes oxidizing with a radicalselected from the group consisting of an OH radical, an HO₂ radical oran O diradical. FIG. 13B illustrates a cross-sectional view of substrate1300 including first and second crystal planes 1304 and 1306,respectively, and having a dielectric layer 1308 formed thereon, inaccordance with an embodiment of the present invention. In anembodiment, first portion 1308A of dielectric layer 1308 is formed onfirst exposed crystal plane 1304 and a second portion 1308B ofdielectric layer 1308 is formed on second exposed crystal plane 1306, asdepicted in FIG. 13B. In one embodiment, the thickness T1 of firstportion 1308A of dielectric layer 1308 is approximately equal to thethickness T2 of second portion 1308B of dielectric layer 1308, eventhough the crystal plane orientation of first exposed crystal plane 1304and second exposed crystal plane 1306 differ. In a specific embodiment,the radical oxidation of substrate 1300 is carried out at a temperatureapproximately in the range of 950-1100 degrees Celsius at a pressureapproximately in the range of 5-15 Torr. In one embodiment, subsequentto forming dielectric layer 1308, substrate 1300 is annealed in theoxidation chamber in an atmosphere including nitrogen at a temperatureapproximately in the range of 900-1100 degrees Celsius for a durationapproximately in the range of 30 seconds-60 seconds.

Thus, a method for fabricating a nonvolatile charge trap memory devicehas been disclosed. In accordance with an embodiment of the presentinvention, a substrate is subjected to a first radical oxidation processto form a first dielectric layer in a first process chamber of a clustertool. A charge-trapping layer may then be deposited above the firstdielectric layer in a second process chamber of the cluster tool. In oneembodiment, the charge-trapping layer is then subjected to a secondradical oxidation process to form a second dielectric layer above thecharge-trapping layer by oxidizing a portion of the charge-trappinglayer in the first process chamber of the cluster tool. By forming alllayers of an oxide-nitride-oxide (ONO) stack in a cluster tool,interface damage may be reduced between the respective layers. Thus, inaccordance with an embodiment of the present invention, an ONO stack isfabricated in a single pass in a cluster tool in order to preserve apristine interface between the layers in the ONO stack. In a specificembodiment, the cluster tool is a single-wafer cluster tool.

1. A method of fabricating a nonvolatile charge trap memory device,comprising: providing a substrate having a charge-trapping layerdisposed thereon; and oxidizing, by exposing the charge-trapping layerto a radical oxidation process, a portion of the charge-trapping layerto form a blocking dielectric layer above the charge-trapping layer. 2.The method of claim 1, wherein the radical oxidation process includesoxidizing with a radical selected from the group consisting of an OHradical, an HO₂ radical and an O diradical.
 3. The method of claim 2,wherein the radical oxidation process is carried out at a temperatureapproximately in the range of 700-800 degrees Celsius at a pressureapproximately in the range of 0.5-5 Torr.
 4. The method of claim 1,wherein the charge-trapping layer comprises a material selected from thegroup consisting of silicon nitride, silicon oxy-nitride, oxygen-richsilicon oxy-nitride and silicon-rich silicon oxy-nitride, and whereinthe blocking dielectric layer comprises silicon dioxide.
 5. The methodof claim 4, wherein the charge-trapping layer comprises a bottomoxygen-rich silicon oxy-nitride portion having a thickness approximatelyin the range of 2.5-3.5 nanometers and a top silicon-rich siliconoxy-nitride portion having a thickness approximately in the range of9-10 nanometers, and wherein oxidizing the portion of thecharge-trapping layer comprises oxidizing the top approximately 2nanometers to approximately 3 nanometers of the top silicon-rich siliconoxy-nitride portion to form the blocking dielectric layer having athickness approximately in the range of 3.5-4.5 nanometers.
 6. Themethod of claim 1, further comprising: annealing the blocking dielectriclayer in an atmosphere comprising a gas selected from the groupconsisting of nitrogen (N₂), nitrous oxide (N₂O), nitrogen dioxide(NO₂), nitric oxide (NO) and ammonia (NH₃) at a temperatureapproximately in the range of 700-800 degrees Celsius.
 7. The method ofclaim 1, wherein the nonvolatile charge trap memory device is aSONOS-type device, and wherein a tunnel dielectric layer is disposedbetween the substrate and the charge-trapping layer.
 8. A method offabricating a nonvolatile charge trap memory device, comprising:providing a substrate in a process chamber; subjecting, in the processchamber, the substrate to a first radical oxidation process to form afirst dielectric layer; subjecting, in the process chamber, thesubstrate to a deposition process to form a charge-trapping layer abovethe first dielectric layer; and subjecting, in the process chamber, thesubstrate to a second radical oxidation process to form a seconddielectric layer above the charge-trapping layer by oxidizing a portionof the charge-trapping layer.
 9. The method of claim 8, wherein both thefirst and the second radical oxidation processes include oxidizing witha radical selected from the group consisting of an OH radical, an HO₂radical and an O diradical.
 10. The method of claim 9, wherein both thefirst and the second radical oxidation processes are carried out at atemperature approximately in the range of 700-800 degrees Celsius at apressure approximately in the range of 0.5-5 Torr.
 11. The method ofclaim 8, wherein the charge-trapping layer comprises a material selectedfrom the group consisting of silicon nitride, silicon oxy-nitride,oxygen-rich silicon oxy-nitride and silicon-rich silicon oxy-nitride,and wherein the second dielectric layer comprises silicon dioxide. 12.The method of claim 11, wherein the charge-trapping layer comprises abottom oxygen-rich silicon oxy-nitride portion having a thicknessapproximately in the range of 2.5-3.5 nanometers and a top silicon-richsilicon oxy-nitride portion having a thickness approximately in therange of 9-10 nanometers, and wherein oxidizing the portion of thecharge-trapping layer comprises oxidizing the top approximately 2nanometers to approximately 3 nanometers of the top silicon-rich siliconoxy-nitride portion to form the second dielectric layer having athickness approximately in the range of 3.5-4.5 nanometers.
 13. Themethod of claim 8, further comprising: annealing, in the processchamber, the second dielectric layer in an atmosphere comprising a gasselected from the group consisting of nitrogen (N₂), nitrous oxide(N₂O), nitrogen dioxide (NO₂), nitric oxide (NO) and ammonia (NH₃) at atemperature approximately in the range of 700-800 degrees Celsius; and,subsequently, depositing a gate layer above the second dielectric layer.14. The method of claim 8, wherein the nonvolatile charge trap memorydevice is a SONOS-type device, wherein the first dielectric layer is atunnel dielectric layer, and wherein the second dielectric layer is ablocking dielectric layer.
 15. The method of claim 8, wherein subjectingthe substrate to the deposition process to form the charge-trappinglayer includes using a gas selected from the group consisting ofdichlorosilane (H₂SiCl₂), bis-(tert-butylamino)silane (BTBAS), ammonia(NH₃) and nitrous oxide (N₂O).
 16. The method of claim 8, wherein theprocess chamber is a low-pressure chemical vapor deposition chamber. 17.A radical oxidation method, comprising: providing a substrate in aprocess chamber; mixing, in the process chamber, hydrogen gas and oxygengas without subjecting the hydrogen gas and oxygen gas to a combustionprocess; and oxidizing, in the process chamber, a portion of thesubstrate with radicals generated from the mixing of the hydrogen gasand oxygen gas.
 18. The method of claim 17, wherein the mixing of thehydrogen gas and oxygen gas and the oxidizing of the portion of thesubstrate are carried out at a temperature approximately in the range of700-800 degrees Celsius at a pressure approximately in the range of0.5-5 Torr.
 19. The method of claim 18, wherein the hydrogen gas andoxygen gas are mixed in an approximate ratio of 1:1.
 20. The method ofclaim 17, wherein the process chamber is a low-pressure chemical vapordeposition chamber.